The present invention relates generally to combustor structures, and more particularly to an improved structure for flame stabilization within a combustor.
Existing combustor and commercial burners generally use recirculating flows to stabilize the flame. Recirculation zones provide regions of low velocity fluid where burning can occur, and provide mixing of fuel, air and hot products and a continuous ignition source that sustains the flame by transporting the hot mixture back towards the face of the combustor. Swirl, bluff bodies and rearward facing steps, or combination of these, are commonly used to create recirculation zones. Swirl is used in most practical combustors and burners. However, swirling flames have undesirably narrow stable operating ranges, and in some applications are long, all a result of aerodynamic instabilities of the recirculation zone and poor fuel and air mixing. Bluff bodies and rearward facing steps are also used to create recirculation zones that promote flame holding in much the same way as swirl stabilized flames. However, recirculation zones behind bluff bodies and rearward facing steps are less stable and have longer flame lengths than those established using swirl. Also, recirculation zones established by bluff bodies or rearward facing steps do not entrain a large quantity of free stream fluid and have a minimal impact on mixing. As a result of these problems, use of bluff bodies and rearward facing steps for flame stabilization is limited to high speed premixed combustion systems such as ramjets and gas turbine engine afterburners.
The invention solves or substantially reduces in critical importance problems with prior state-of-the-art combustor structures by providing a flame stabilizing structure comprising two or more bluff bodies in tandem or otherwise defining a cavity within which a trapped vortex defines a stable recirculation zone, with fuel and air injection directly into the recirculation zone, to sustain the flame. The invention provides flame stabilization within wide ranges of fuel and air flow conditions not achievable within previously existing structures. The invention further provides a simple and compact structure within which the fuel to air ratio may be controlled in the trapped vortex independently of the incoming air and fuel flow rates, which feature provides active combustion control and stable combustion with high efficiency and low exhaust pollutants over a wider range of operating conditions than are achievable in conventional combustor structures.
It is therefore a principal object of the invention to provide a simple, compact and low cost flame stabilizing structure for a combustor that allows stable operation over a wide range of fuel and air flow conditions with low lean blow-out limits, good relight capabilities and low specific fuel consumption.
It is a further object of the invention to provide an efficient, low pressure drop, low polluting flame stabilization structure for a combustor.
It is yet another object of the invention to provide an improved flame stabilizing combustion source structure for gas turbine combustors, afterburners, ramjet combustors, flight line heaters, commercial boilers, furnaces, waste incinerators, and the like.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.